Computing devices, such as notebook computers, personal data assistants (PDAs), and mobile handsets, have user interface devices, which are also known as human interface devices (HID). One type of user interface devices that has become more common is touch-sensing devices, such as touch-sensor pads (also commonly referred to as touchpads), touch-sensor sliders, touch-sensor buttons, touch-sensor keyboard, touchsreens, and touchpanels. There are a number of types of touch sensing technology, such as optical imaging, resistive, surface wave, capacitive, infrared, dispersive signal, and strain gauge technologies.
In general, capacitance-sensing devices may replace mechanical buttons, knobs, and other similar mechanical user interface controls. Capacitance-sensing devices eliminate the complicated mechanical switches and buttons, providing reliable operation under harsh conditions. In addition, capacitance-sensing devices are widely used in modern customer applications, providing new user interface options in existing products.
A typical capacitance-sensing device includes one or more sense elements that form a touch-sensing surface and capacitance-sensing circuitry configured to measure the capacitance on the one or more sense elements. The sense elements of the capacitance-sensing devices can be arranged in the form of an array for the touch-sensing surface. When a touch object, such as a finger, comes in close proximity or physical contact with the touch-sensing surface, capacitance-sensing circuitry measures capacitances on the one or more sense elements of the touch-sensing surface. The capacitance-sensing circuitry also measures the capacitances when the touch object is not in proximity or in contact to establish baseline or reference level of capacitance. The measured capacitance(s) can be converted into digital values, and the digital values can be used, for example, to detect a presence of a touch object, measure distance, speed, and acceleration of the touch object on the touch-sensing surface, as well as detecting gestures of the touch object.